#!/usr/bin/env python

# Copyright 2016, The Android Open Source Project
#
# Licensed under the Apache License, Version 2.0 (the "License");
# you may not use this file except in compliance with the License.
# You may obtain a copy of the License at
#
#     http://www.apache.org/licenses/LICENSE-2.0
#
# Unless required by applicable law or agreed to in writing, software
# distributed under the License is distributed on an "AS IS" BASIS,
# WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
# See the License for the specific language governing permissions and
# limitations under the License.


"""Command-line tool for partitioning Brillo images."""


import argparse
import copy
import json
import math
import numbers
import struct
import sys
import uuid
import zlib

# Python 2.6 required for modern exception syntax
if sys.hexversion < 0x02060000:
  print >> sys.stderr, "Python 2.6 or newer is required."
  sys.exit(1)

# Keywords used in JSON files.
JSON_KEYWORD_SETTINGS = 'settings'
JSON_KEYWORD_SETTINGS_AB_SUFFIXES = 'ab_suffixes'
JSON_KEYWORD_SETTINGS_DISK_SIZE = 'disk_size'
JSON_KEYWORD_SETTINGS_DISK_ALIGNMENT = 'disk_alignment'
JSON_KEYWORD_SETTINGS_DISK_GUID = 'disk_guid'
JSON_KEYWORD_SETTINGS_PARTITIONS_OFFSET_BEGIN = 'partitions_offset_begin'
JSON_KEYWORD_PARTITIONS = 'partitions'
JSON_KEYWORD_PARTITIONS_LABEL = 'label'
JSON_KEYWORD_PARTITIONS_OFFSET = 'offset'
JSON_KEYWORD_PARTITIONS_SIZE = 'size'
JSON_KEYWORD_PARTITIONS_GROW = 'grow'
JSON_KEYWORD_PARTITIONS_GUID = 'guid'
JSON_KEYWORD_PARTITIONS_TYPE_GUID = 'type_guid'
JSON_KEYWORD_PARTITIONS_FLAGS = 'flags'
JSON_KEYWORD_PARTITIONS_PERSIST = 'persist'
JSON_KEYWORD_PARTITIONS_IGNORE = 'ignore'
JSON_KEYWORD_PARTITIONS_AB = 'ab'
JSON_KEYWORD_PARTITIONS_AB_EXPANDED = 'ab_expanded'
JSON_KEYWORD_PARTITIONS_POSITION = 'position'
JSON_KEYWORD_AUTO = 'auto'

# Possible values for the --type option of the query_partition
# sub-command.
QUERY_PARTITION_TYPES = ['size',
                         'offset',
                         'guid',
                         'type_guid',
                         'flags',
                         'persist']

BPT_VERSION_MAJOR = 1
BPT_VERSION_MINOR = 0

DISK_SECTOR_SIZE = 512

GPT_NUM_LBAS = 33

GPT_MIN_PART_NUM = 1
GPT_MAX_PART_NUM = 128

KNOWN_TYPE_GUIDS = {
    'brillo_boot': 'bb499290-b57e-49f6-bf41-190386693794',
    'brillo_bootloader': '4892aeb3-a45f-4c5f-875f-da3303c0795c',
    'brillo_system': '0f2778c4-5cc1-4300-8670-6c88b7e57ed6',
    'brillo_odm': 'e99d84d7-2c1b-44cf-8c58-effae2dc2558',
    'brillo_oem': 'aa3434b2-ddc3-4065-8b1a-18e99ea15cb7',
    'brillo_userdata': '0bb7e6ed-4424-49c0-9372-7fbab465ab4c',
    'brillo_misc': '6b2378b0-0fbc-4aa9-a4f6-4d6e17281c47',
    'brillo_vbmeta': 'b598858a-5fe3-418e-b8c4-824b41f4adfc',
    'brillo_vendor_specific': '314f99d5-b2bf-4883-8d03-e2f2ce507d6a',
    'linux_fs': '0fc63daf-8483-4772-8e79-3d69d8477de4',
    'ms_basic_data': 'ebd0a0a2-b9e5-4433-87c0-68b6b72699c7',
    'efi_system': 'c12a7328-f81f-11d2-ba4b-00a0c93ec93b'
}


def RoundToMultiple(number, size, round_down=False):
  """Rounds a number up (or down) to nearest multiple of another number.

  Args:
    number: The number to round up.
    size: The multiple to round up to.
    round_down: If True, the number will be rounded down.

  Returns:
    If |number| is a multiple of |size|, returns |number|, otherwise
    returns |number| + |size| - |remainder| (if |round_down| is False) or
    |number| - |remainder| (if |round_down| is True). Always returns
    an integer.
  """
  remainder = number % size
  if remainder == 0:
    return int(number)
  if round_down:
    return int(number - remainder)
  return int(number + size - remainder)


def ParseNumber(arg):
  """Number parser.

  If |arg| is an integer, that value is returned. Otherwise int(arg, 0)
  is returned.

  This function is suitable for use in the |type| parameter of
  |ArgumentParser|'s add_argument() function. An improvement to just
  using type=int is that this function supports numbers in other
  bases, e.g. "0x1234".

  Arguments:
    arg: Argument (int or string) to parse.

  Returns:
    The parsed value, as an integer.

  Raises:
    ValueError: If the argument could not be parsed.
  """
  if isinstance(arg, numbers.Integral):
    return arg
  return int(arg, 0)


def ParseGuid(arg):
  """Parser for RFC 4122 GUIDs.

  Arguments:
    arg: The argument, as a string.

  Returns:
    UUID in hyphenated format.

  Raises:
    ValueError: If the given string cannot be parsed.
  """
  return str(uuid.UUID(arg))


def ParseSize(arg):
  """Parser for size strings with decimal and binary unit support.

  This supports both integers and strings.

  Arguments:
    arg: The string to parse.

  Returns:
    The parsed size in bytes as an integer.

  Raises:
    ValueError: If the given string cannot be parsed.
  """
  if isinstance(arg, numbers.Integral):
    return arg

  ws_index = arg.find(' ')
  if ws_index != -1:
    num = float(arg[0:ws_index])
    factor = 1
    if arg.endswith('KiB'):
      factor = 1024
    elif arg.endswith('MiB'):
      factor = 1024*1024
    elif arg.endswith('GiB'):
      factor = 1024*1024*1024
    elif arg.endswith('TiB'):
      factor = 1024*1024*1024*1024
    elif arg.endswith('PiB'):
      factor = 1024*1024*1024*1024*1024
    elif arg.endswith('kB'):
      factor = 1000
    elif arg.endswith('MB'):
      factor = 1000*1000
    elif arg.endswith('GB'):
      factor = 1000*1000*1000
    elif arg.endswith('TB'):
      factor = 1000*1000*1000*1000
    elif arg.endswith('PB'):
      factor = 1000*1000*1000*1000*1000
    else:
      raise ValueError('Cannot parse string "{}"'.format(arg))
    value = num*factor
    # If the resulting value isn't an integer, round up.
    if not value.is_integer():
      value = int(math.ceil(value))
  else:
    value = int(arg, 0)
  return value


class GuidGenerator(object):
  """An interface for obtaining strings that are GUIDs.

  To facilitate unit testing, this abstraction is used instead of the
  directly using the uuid module.
  """

  def dispense_guid(self, partition_number):
    """Dispenses a GUID.

    Arguments:
      partition_number: The partition number or 0 if requesting a GUID
                        for the whole disk.

    Returns:
      A RFC 4122 compliant GUID, as a string.
    """
    return str(uuid.uuid4())


class Partition(object):
  """Object representing a partition.

  Attributes:
    label: The partition label.
    offset: Offset of the partition on the disk, or None.
    size: Size of the partition or None if not specified.
    grow: True if partition has been requested to use all remaining space.
    guid: Instance GUID (RFC 4122 compliant) as a string or None or 'auto'
          if it should be automatically generated.
    type_guid: Type GUID (RFC 4122 compliant) as a string or a known type
               from the |KNOWN_TYPE_GUIDS| map.
    flags: GUID flags.
    persist: If true, sets bit 0 of flags indicating that this partition should
             not be deleted by the bootloader.
    ab: If True, the partition is an A/B partition.
    ab_expanded: If True, the A/B partitions have been generated.
    ignore: If True, the partition should not be included in the final output.
    position: The requested position of the partition or 0 if it doesn't matter.
  """

  def __init__(self):
    """Initializer method."""
    self.label = ''
    self.offset = None
    self.size = None
    self.grow = False
    self.guid = None
    self.type_guid = None
    self.flags = 0
    self.persist = False
    self.ab = False
    self.ab_expanded = False
    self.ignore = False
    self.position = 0

  def add_info(self, pobj):
    """Add information to partition.

    Arguments:
      pobj: A JSON object with information about the partition.
    """
    self.label = pobj[JSON_KEYWORD_PARTITIONS_LABEL]
    value = pobj.get(JSON_KEYWORD_PARTITIONS_OFFSET)
    if value is not None:
      self.offset = ParseSize(value)
    value = pobj.get(JSON_KEYWORD_PARTITIONS_SIZE)
    if value is not None:
      self.size = ParseSize(value)
    value = pobj.get(JSON_KEYWORD_PARTITIONS_GROW)
    if value is not None:
      self.grow = value
    value = pobj.get(JSON_KEYWORD_PARTITIONS_AB)
    if value is not None:
      self.ab = value
    value = pobj.get(JSON_KEYWORD_PARTITIONS_AB_EXPANDED)
    if value is not None:
      self.ab_expanded = value
    value = pobj.get(JSON_KEYWORD_PARTITIONS_GUID)
    if value is not None:
      self.guid = value
    value = pobj.get(JSON_KEYWORD_PARTITIONS_IGNORE)
    if value is not None:
      self.ignore = value
    value = pobj.get(JSON_KEYWORD_PARTITIONS_TYPE_GUID)
    if value is not None:
      self.type_guid = str.lower(str(value))
      if self.type_guid in KNOWN_TYPE_GUIDS:
        self.type_guid = KNOWN_TYPE_GUIDS[self.type_guid]
    value = pobj.get(JSON_KEYWORD_PARTITIONS_FLAGS)
    if value is not None:
      self.flags = ParseNumber(value)
    value = pobj.get(JSON_KEYWORD_PARTITIONS_PERSIST)
    if value is not None:
      self.persist = value
      if value:
        self.flags = self.flags | 0x1
    value = pobj.get(JSON_KEYWORD_PARTITIONS_POSITION)
    if value is not None:
      self.position = ParseNumber(value)

  def expand_guid(self, guid_generator, partition_number):
    """Assign instance GUID and type GUID if required.

    Arguments:
      guid_generator: A GuidGenerator object.
      partition_number: The partition number, starting from 1.
    """
    if not self.guid or self.guid == JSON_KEYWORD_AUTO:
      self.guid = guid_generator.dispense_guid(partition_number)
    if not self.type_guid:
      self.type_guid = KNOWN_TYPE_GUIDS['brillo_vendor_specific']

  def validate(self):
    """Sanity checks data in object."""

    try:
      _ = uuid.UUID(str(self.guid))
    except ValueError:
      raise ValueError('The string "{}" is not a valid GPT instance GUID on '
                       'partition with label "{}".'.format(
                           str(self.guid), self.label))

    try:
      _ = uuid.UUID(str(self.type_guid))
    except ValueError:
      raise ValueError('The string "{}" is not a valid GPT type GUID on '
                       'partition with label "{}".'.format(
                           str(self.type_guid), self.label))

    if not self.size:
      if not self.grow:
        raise ValueError('Size can only be unset if "grow" is True.')

  def cmp(self, other):
    """Comparison method."""
    self_position = self.position
    if self_position == 0:
      self_position = GPT_MAX_PART_NUM
    other_position = other.position
    if other_position == 0:
      other_position = GPT_MAX_PART_NUM
    return cmp(self_position, other_position)


class Settings(object):
  """An object for holding settings.

  Attributes:
    ab_suffixes: A list of A/B suffixes to use.
    disk_size: An integer with the disk size in bytes.
    partitions_offset_begin: An integer with the disk partitions
                             offset begin size in bytes.
    disk_alignment: The alignment to use for partitions.
    disk_guid: The GUID to use for the disk or None or 'auto' if
               automatically generated.
  """

  def __init__(self):
    """Initializer with defaults."""
    self.ab_suffixes = ['_a', '_b']
    self.disk_size = None
    self.partitions_offset_begin = 0
    self.disk_alignment = 4096
    self.disk_guid = JSON_KEYWORD_AUTO


class BptError(Exception):
  """Application-specific errors.

  These errors represent issues for which a stack-trace should not be
  presented.

  Attributes:
    message: Error message.
  """

  def __init__(self, message):
    Exception.__init__(self, message)


class BptParsingError(BptError):
  """Represents an error with an input file.

  Attributes:
    message: Error message.
    filename: Name of the file that caused an error.
  """

  def __init__(self, filename, message):
    self.filename = filename
    BptError.__init__(self, message)


class Bpt(object):
  """Business logic for bpttool command-line tool."""

  def _read_json(self, input_files, ab_collapse=True):
    """Parses a stack of JSON files into suitable data structures.

    The order of files matters as later files can modify partitions
    declared in earlier files.

    Arguments:
      input_files: An ordered list of open files.
      ab_collapse: If True, collapse A/B partitions.

    Returns:
      A tuple where the first element is a list of Partition objects
      and the second element is a Settings object.

    Raises:
      BptParsingError: If an input file has an error.
    """
    partitions = []
    settings = Settings()

    # Read all input file and merge partitions and settings.
    for f in input_files:
      try:
        obj = json.loads(f.read())
      except ValueError as e:
        # Unfortunately we can't easily get the line number where the
        # error occurred.
        raise BptParsingError(f.name, e.message)

      sobj = obj.get(JSON_KEYWORD_SETTINGS)
      if sobj:
        ab_suffixes = sobj.get(JSON_KEYWORD_SETTINGS_AB_SUFFIXES)
        if ab_suffixes:
          settings.ab_suffixes = ab_suffixes
        disk_size = sobj.get(JSON_KEYWORD_SETTINGS_DISK_SIZE)
        if disk_size:
          settings.disk_size = ParseSize(disk_size)
        partitions_offset_begin = sobj.get(
                JSON_KEYWORD_SETTINGS_PARTITIONS_OFFSET_BEGIN)
        if partitions_offset_begin:
          settings.partitions_offset_begin = ParseSize(partitions_offset_begin)
        disk_alignment = sobj.get(JSON_KEYWORD_SETTINGS_DISK_ALIGNMENT)
        if disk_alignment:
          settings.disk_alignment = ParseSize(disk_alignment)
        disk_guid = sobj.get(JSON_KEYWORD_SETTINGS_DISK_GUID)
        if disk_guid:
          settings.disk_guid = disk_guid

      pobjs = obj.get(JSON_KEYWORD_PARTITIONS)
      if pobjs:
        for pobj in pobjs:
          if ab_collapse and pobj.get(JSON_KEYWORD_PARTITIONS_AB_EXPANDED):
            # If we encounter an expanded partition, unexpand it. This
            # is to make it possible to use output-JSON (from this tool)
            # and stack it with an input-JSON file that e.g. specifies
            # size='256 GiB' for the 'system' partition.
            label = pobj[JSON_KEYWORD_PARTITIONS_LABEL]
            if label.endswith(settings.ab_suffixes[0]):
              # Modify first A/B copy so it doesn't have the trailing suffix.
              new_len = len(label) - len(settings.ab_suffixes[0])
              pobj[JSON_KEYWORD_PARTITIONS_LABEL] = label[0:new_len]
              pobj[JSON_KEYWORD_PARTITIONS_AB_EXPANDED] = False
              pobj[JSON_KEYWORD_PARTITIONS_GUID] = JSON_KEYWORD_AUTO
            else:
              # Skip other A/B copies.
              continue
          # Find or create a partition.
          p = None
          for candidate in partitions:
            if candidate.label == pobj[JSON_KEYWORD_PARTITIONS_LABEL]:
              p = candidate
              break
          if not p:
            p = Partition()
            partitions.append(p)
          p.add_info(pobj)

    return partitions, settings

  def _generate_json(self, partitions, settings):
    """Generate a string with JSON representing partitions and settings.

    Arguments:
      partitions: A list of Partition objects.
      settings: A Settings object.

    Returns:
      A JSON string.
    """
    suffixes_str = '['
    for n in range(0, len(settings.ab_suffixes)):
      if n != 0:
        suffixes_str += ', '
      suffixes_str += '"{}"'.format(settings.ab_suffixes[n])
    suffixes_str += ']'

    ret = ('{{\n'
           '  "' + JSON_KEYWORD_SETTINGS + '": {{\n'
           '    "' + JSON_KEYWORD_SETTINGS_AB_SUFFIXES + '": {},\n'
           '    "' + JSON_KEYWORD_SETTINGS_PARTITIONS_OFFSET_BEGIN + '": {},\n'
           '    "' + JSON_KEYWORD_SETTINGS_DISK_SIZE + '": {},\n'
           '    "' + JSON_KEYWORD_SETTINGS_DISK_ALIGNMENT + '": {},\n'
           '    "' + JSON_KEYWORD_SETTINGS_DISK_GUID + '": "{}"\n'
           '  }},\n'
           '  "' + JSON_KEYWORD_PARTITIONS + '": [\n').format(
               suffixes_str,
               settings.partitions_offset_begin,
               settings.disk_size,
               settings.disk_alignment,
               settings.disk_guid)

    for n in range(0, len(partitions)):
      p = partitions[n]
      ret += ('    {{\n'
              '      "' + JSON_KEYWORD_PARTITIONS_LABEL + '": "{}",\n'
              '      "' + JSON_KEYWORD_PARTITIONS_OFFSET + '": {},\n'
              '      "' + JSON_KEYWORD_PARTITIONS_SIZE + '": {},\n'
              '      "' + JSON_KEYWORD_PARTITIONS_GROW + '": {},\n'
              '      "' + JSON_KEYWORD_PARTITIONS_GUID + '": "{}",\n'
              '      "' + JSON_KEYWORD_PARTITIONS_TYPE_GUID + '": "{}",\n'
              '      "' + JSON_KEYWORD_PARTITIONS_FLAGS + '": "{:#018x}",\n'
              '      "' + JSON_KEYWORD_PARTITIONS_PERSIST + '": {},\n'
              '      "' + JSON_KEYWORD_PARTITIONS_IGNORE + '": {},\n'
              '      "' + JSON_KEYWORD_PARTITIONS_AB + '": {},\n'
              '      "' + JSON_KEYWORD_PARTITIONS_AB_EXPANDED + '": {},\n'
              '      "' + JSON_KEYWORD_PARTITIONS_POSITION + '": {}\n'
              '    }}{}\n').format(p.label,
                                   p.offset,
                                   p.size,
                                   'true' if p.grow else 'false',
                                   p.guid,
                                   p.type_guid,
                                   p.flags,
                                   'true' if p.persist else 'false',
                                   'true' if p.ignore else 'false',
                                   'true' if p.ab else 'false',
                                   'true' if p.ab_expanded else 'false',
                                   p.position,
                                   '' if n == len(partitions) - 1 else ',')
    ret += ('  ]\n'
            '}\n')
    return ret

  def _lba_to_chs(self, lba):
    """Converts LBA to CHS.

    Arguments:
      lba: The sector number to convert.

    Returns:
      An array containing the CHS encoded the way it's expected in a
      MBR partition table.
    """
    # See https://en.wikipedia.org/wiki/Cylinder-head-sector
    num_heads = 255
    num_sectors = 63
    # If LBA isn't going to fit in CHS, return maximum CHS values.
    max_lba = 255*num_heads*num_sectors
    if lba > max_lba:
      return [255, 255, 255]
    c = lba / (num_heads*num_sectors)
    h = (lba / num_sectors) % num_heads
    s = lba % num_sectors
    return [h, (((c>>8) & 0x03)<<6) | (s & 0x3f), c & 0xff]

  def _generate_protective_mbr(self, settings):
    """Generate Protective MBR.

    Arguments:
      settings: A Settings object.

    Returns:
      A string with the binary protective MBR (512 bytes).
    """
    # See https://en.wikipedia.org/wiki/Master_boot_record for MBR layout.
    #
    # The first partition starts at offset 446 (0x1be).
    lba_start = 1
    lba_end = settings.disk_size/DISK_SECTOR_SIZE - 1
    start_chs = self._lba_to_chs(lba_start)
    end_chs = self._lba_to_chs(lba_end)
    pmbr = struct.pack('<446s'     # Bootloader code
                       'B'         # Status.
                       'BBB'       # CHS start.
                       'B'         # Partition type.
                       'BBB'       # CHS end.
                       'I'         # LBA of partition start.
                       'I'         # Number of sectors in partition.
                       '48x'       # Padding to get to offset 510 (0x1fe).
                       'BB',       # Boot signature.
                       '\xfa\xeb\xfe', # cli ; jmp $ (x86)
                       0x00,
                       start_chs[0], start_chs[1], start_chs[2],
                       0xee,       # MBR Partition Type: GPT protective MBR.
                       end_chs[0], end_chs[1], end_chs[2],
                       1,          # LBA start
                       lba_end,
                       0x55, 0xaa)
    return pmbr

  def _generate_gpt(self, partitions, settings, primary=True):
    """Generate GUID Partition Table.

    Arguments:
      partitions: A list of Partition objects.
      settings: A Settings object.
      primary: True to generate primary GPT, False to generate secondary.

    Returns:
      A string with the binary GUID Partition Table (33*512 bytes).
    """
    # See https://en.wikipedia.org/wiki/Master_boot_record for MBR layout.
    #
    # The first partition starts at offset 446 (0x1be).

    disk_num_lbas = settings.disk_size/DISK_SECTOR_SIZE
    if primary:
      current_lba = 1
      other_lba = disk_num_lbas - 1
      partitions_lba = 2
    else:
      current_lba = disk_num_lbas - 1
      other_lba = 1
      partitions_lba = disk_num_lbas - GPT_NUM_LBAS
    first_usable_lba = GPT_NUM_LBAS + 1
    last_usable_lba = disk_num_lbas - GPT_NUM_LBAS - 1

    part_array = []
    for p in partitions:
      part_array.append(struct.pack(
          '<16s'    # Partition type GUID.
          '16s'     # Partition instance GUID.
          'QQ'      # First and last LBA.
          'Q'       # Flags.
          '72s',    # Name (36 UTF-16LE code units).
          uuid.UUID(p.type_guid).get_bytes_le(),
          uuid.UUID(p.guid).get_bytes_le(),
          p.offset/DISK_SECTOR_SIZE,
          (p.offset + p.size)/DISK_SECTOR_SIZE - 1,
          p.flags,
          p.label.encode(encoding='utf-16le')))

    part_array.append(((128 - len(partitions))*128) * '\0')
    part_array_str = ''.join(part_array)

    partitions_crc32 = zlib.crc32(part_array_str) % (1<<32)

    header_crc32 = 0
    while True:
      header = struct.pack(
          '<8s'    # Signature.
          '4B'     # Version.
          'I'      # Header size.
          'I'      # CRC32 (must be zero during calculation).
          'I'      # Reserved (must be zero).
          'QQ'     # Current and Other LBA.
          'QQ'     # First and last usable LBA.
          '16s'    # Disk GUID.
          'Q'      # Starting LBA of array of partitions.
          'I'      # Number of partitions.
          'I'      # Partition entry size, in bytes.
          'I'      # CRC32 of partition array
          '420x',  # Padding to get to 512 bytes.
          'EFI PART',
          0x00, 0x00, 0x01, 0x00,
          92,
          header_crc32,
          0x00000000,
          current_lba, other_lba,
          first_usable_lba, last_usable_lba,
          uuid.UUID(settings.disk_guid).get_bytes_le(),
          partitions_lba,
          128,
          128,
          partitions_crc32)
      if header_crc32 != 0:
        break
      header_crc32 = zlib.crc32(header[0:92]) % (1<<32)

    if primary:
      return header + part_array_str
    else:
      return part_array_str + header

  def _generate_gpt_bin(self, partitions, settings):
    """Generate a bytearray representing partitions and settings.

    The blob will have three partition tables, laid out one after
    another: 1) Protective MBR (512 bytes); 2) Primary GPT (33*512
    bytes); and 3) Secondary GPT (33*512 bytes).

    The total size will be 34,304 bytes.

    Arguments:
      partitions: A list of Partition objects.
      settings: A Settings object.

    Returns:
      A bytearray() object.
    """
    protective_mbr = self._generate_protective_mbr(settings)
    primary_gpt = self._generate_gpt(partitions, settings)
    secondary_gpt = self._generate_gpt(partitions, settings, primary=False)
    ret = protective_mbr + primary_gpt + secondary_gpt
    return ret

  def _validate_disk_partitions(self, partitions, disk_size):
    """Check that a list of partitions have assigned offsets and fits on a
       disk of a given size.

    This function checks partition offsets and sizes to see if they may fit on
    a disk image.

    Arguments:
      partitions: A list of Partition objects.
      settings: Integer size of disk image.

    Raises:
      BptError: If checked condition is not satisfied.
    """
    for p in partitions:
      if not p.offset or p.offset < (GPT_NUM_LBAS + 1)*DISK_SECTOR_SIZE:
        raise BptError('Partition with label "{}" has no offset.'
                       .format(p.label))
      if not p.size or p.size < 0:
        raise BptError('Partition with label "{}" has no size.'
                        .format(p.label))
      if (p.offset + p.size) > (disk_size - GPT_NUM_LBAS*DISK_SECTOR_SIZE):
        raise BptError('Partition with label "{}" exceeds the disk '
                       'image size.'.format(p.label))

  def make_table(self,
                 inputs,
                 ab_suffixes=None,
                 partitions_offset_begin=None,
                 disk_size=None,
                 disk_alignment=None,
                 disk_guid=None,
                 guid_generator=None):
    """Implementation of the 'make_table' command.

    This function takes a list of input partition definition files,
    flattens them, expands A/B partitions, grows partitions, and lays
    out partitions according to alignment constraints.

    Arguments:
      inputs: List of JSON files to parse.
      ab_suffixes: List of the A/B suffixes (as a comma-separated string)
                   to use or None to not override.
      partitions_offset_begin: Size of disk partitions offset
                               begin or None to not override.
      disk_size: Size of disk or None to not override.
      disk_alignment: Disk alignment or None to not override.
      disk_guid: Disk GUID as a string or None to not override.
      guid_generator: A GuidGenerator or None to use the default.

    Returns:
      A tuple where the first argument is a JSON string for the resulting
      partitions and the second argument is the binary partition tables.

    Raises:
      BptParsingError: If an input file has an error.
      BptError: If another application-specific error occurs
    """
    partitions, settings = self._read_json(inputs)

    # Command-line arguments override anything specified in input
    # files.
    if disk_size:
      settings.disk_size = int(math.ceil(disk_size))
    if disk_alignment:
      settings.disk_alignment = int(disk_alignment)
    if partitions_offset_begin:
      settings.partitions_offset_begin = int(partitions_offset_begin)
    if ab_suffixes:
      settings.ab_suffixes = ab_suffixes.split(',')
    if disk_guid:
      settings.disk_guid = disk_guid

    if not guid_generator:
      guid_generator = GuidGenerator()

    # We need to know the disk size. Also round it down to ensure it's
    # a multiple of the sector size.
    if not settings.disk_size:
      raise BptError('Disk size not specified. Use --disk_size option '
                     'or specify it in an input file.\n')
    settings.disk_size = RoundToMultiple(settings.disk_size,
                                         DISK_SECTOR_SIZE,
                                         round_down=True)

    # Alignment must be divisible by disk sector size.
    if settings.disk_alignment % DISK_SECTOR_SIZE != 0:
      raise BptError(
          'Disk alignment size of {} is not divisible by {}.\n'.format(
              settings.disk_alignment, DISK_SECTOR_SIZE))

    if settings.partitions_offset_begin != 0:
      # Disk partitions offset begin size must be
      # divisible by disk sector size.
      if settings.partitions_offset_begin % settings.disk_alignment != 0:
        raise BptError(
            'Disk Partitions offset begin size of {} '
            'is not divisible by {}.\n'.format(
                settings.partitions_offset_begin, settings.disk_alignment))
      settings.partitions_offset_begin = max(settings.partitions_offset_begin,
                                           DISK_SECTOR_SIZE*(1 + GPT_NUM_LBAS))
      settings.partitions_offset_begin = RoundToMultiple(
          settings.partitions_offset_begin, settings.disk_alignment)

    # Expand A/B partitions and skip ignored partitions.
    expanded_partitions = []
    for p in partitions:
      if p.ignore:
        continue
      if p.ab and not p.ab_expanded:
        p.ab_expanded = True
        for suffix in settings.ab_suffixes:
          new_p = copy.deepcopy(p)
          new_p.label += suffix
          expanded_partitions.append(new_p)
      else:
        expanded_partitions.append(p)
    partitions = expanded_partitions

    # Expand Disk GUID if needed.
    if not settings.disk_guid or settings.disk_guid == JSON_KEYWORD_AUTO:
      settings.disk_guid = guid_generator.dispense_guid(0)

    # Sort according to 'position' attribute.
    partitions = sorted(partitions, cmp=lambda x, y: x.cmp(y))

    # Automatically generate GUIDs if the GUID is unset or set to
    # 'auto'. Also validate the rest of the fields.
    part_no = 1
    for p in partitions:
      p.expand_guid(guid_generator, part_no)
      p.validate()
      part_no += 1

    # Idenfify partition to grow and lay out partitions, ignoring the
    # one to grow. This way we can figure out how much space is left.
    #
    # Right now we only support a single 'grow' partition but we could
    # support more in the future by splitting up the available bytes
    # between them.
    grow_part = None
    # offset minimal size: DISK_SECTOR_SIZE*(1 + GPT_NUM_LBAS)
    offset = max(settings.partitions_offset_begin,
                 DISK_SECTOR_SIZE*(1 + GPT_NUM_LBAS))
    for p in partitions:
      if p.grow:
        if grow_part:
          raise BptError('Only a single partition can be automatically '
                         'grown.\n')
        grow_part = p
      else:
        # Ensure size is a multiple of DISK_SECTOR_SIZE by rounding up
        # (user may specify it as e.g. "1.5 GB" which is not divisible
        # by 512).
        p.size = RoundToMultiple(p.size, DISK_SECTOR_SIZE)
        # Align offset to disk alignment.
        offset = RoundToMultiple(offset, settings.disk_alignment)
        offset += p.size

    # After laying out (respecting alignment) all non-grow
    # partitions, check that the given disk size is big enough.
    if offset > settings.disk_size - DISK_SECTOR_SIZE*GPT_NUM_LBAS:
      raise BptError('Disk size of {} bytes is too small for partitions '
                     'totaling {} bytes.\n'.format(
                         settings.disk_size, offset))

    # If we have a grow partition, it'll starts at the next
    # available alignment offset and we can calculate its size as
    # follows.
    if grow_part:
      offset = RoundToMultiple(offset, settings.disk_alignment)
      grow_part.size = RoundToMultiple(
          settings.disk_size - DISK_SECTOR_SIZE*GPT_NUM_LBAS - offset,
          settings.disk_alignment,
          round_down=True)
      if grow_part.size < DISK_SECTOR_SIZE:
        raise BptError('Not enough space for partition "{}" to be '
                       'automatically grown.\n'.format(grow_part.label))

    # Now we can assign partition start offsets for all partitions,
    # including the grow partition.
    # offset minimal size: DISK_SECTOR_SIZE*(1 + GPT_NUM_LBAS)
    offset = max(settings.partitions_offset_begin,
                 DISK_SECTOR_SIZE*(1 + GPT_NUM_LBAS))
    for p in partitions:
      # Align offset.
      offset = RoundToMultiple(offset, settings.disk_alignment)
      p.offset = offset
      offset += p.size
    assert offset <= settings.disk_size - DISK_SECTOR_SIZE*GPT_NUM_LBAS

    json_str = self._generate_json(partitions, settings)

    gpt_bin = self._generate_gpt_bin(partitions, settings)

    return json_str, gpt_bin

  def make_disk_image(self, output, bpt, images, allow_empty_partitions=False):
    """Implementation of the 'make_disk_image' command.

    This function takes in a list of partitions images and a bpt file
    for the purpose of creating a raw disk image with a protective MBR,
    primary and secondary GPT, and content for each partition as specified.

    Arguments:
      output: Output file where disk image is to be written to.
      bpt: BPT JSON file to parse.
      images: List of partition image paths to be combined (as specified by
              bpt).  Each element is of the form.
              'PARTITION_NAME:/PATH/TO/PARTITION_IMAGE'
      allow_empty_partitions: If True, partitions defined in |bpt| need not to
                              be present in |images|. Otherwise an exception is
                              thrown if a partition is referenced in |bpt| but
                              not in |images|.

    Raises:
      BptParsingError: If an image file has an error.
      BptError: If another application-specific error occurs.
    """
    # Generate partition list and settings.
    partitions, settings = self._read_json([bpt], ab_collapse=False)

    # Validated partition sizes and offsets.
    self._validate_disk_partitions(partitions, settings.disk_size)

    # Sort according to 'offset' attribute.
    partitions = sorted(partitions, cmp=lambda x, y: cmp(x.offset, y.offset))

    # Create necessary tables.
    protective_mbr = self._generate_protective_mbr(settings)
    primary_gpt = self._generate_gpt(partitions, settings)
    secondary_gpt = self._generate_gpt(partitions, settings, primary=False)

    # Start at 0 offset for mbr and primary gpt.
    output.seek(0)
    output.write(protective_mbr)
    output.write(primary_gpt)

    # Create mapping of partition name to partition image file.
    image_file_names = {}
    try:
      for name_path in images:
        name, path = name_path.split(":")
        image_file_names[name] = path
    except ValueError as e:
      raise BptParsingError(name_path, 'Bad image argument {}.'.format(
                            images[i]))

    # Read image and insert in correct offset.
    for p in partitions:
      if p.label not in image_file_names:
        if allow_empty_partitions:
          continue
        else:
          raise BptParsingError(bpt.name, 'No content specified for partition'
                                ' with label {}'.format(p.label))

      with open(image_file_names[p.label], 'rb') as partition_image:
        output.seek(p.offset)
        partition_blob = partition_image.read()
        if len(partition_blob) > p.size:
          raise BptError('Partition image content with label "{}" exceeds the '
                         'partition size.'.format(p.label))
        output.write(partition_blob)

    # Put secondary GPT and end of disk.
    output.seek(settings.disk_size - len(secondary_gpt))
    output.write(secondary_gpt)

  def query_partition(self, input_file, part_label, query_type, ab_collapse):
    """Implementation of the 'query_partition' command.

    This reads the partition definition file given by |input_file| and
    returns information of type |query_type| for the partition with
    label |part_label|.

    Arguments:
      input_file: A JSON file to parse.
      part_label: Label of partition to query information about.
      query_type: The information to query, see |QUERY_PARTITION_TYPES|.
      ab_collapse: If True, collapse A/B partitions.

    Returns:
      The requested information as a string or None if there is no
      partition with the given label.

    Raises:
      BptParsingError: If an input file has an error.
      BptError: If another application-specific error occurs
    """

    partitions, _ = self._read_json([input_file], ab_collapse)

    part = None
    for p in partitions:
      if p.label == part_label:
        part = p
        break

    if not part:
      return None

    value = part.__dict__.get(query_type)
    # Print out flags as a hex-value.
    if query_type == 'flags':
      return '{:#018x}'.format(value)
    return str(value)


class BptTool(object):
  """Object for bpttool command-line tool."""

  def __init__(self):
    """Initializer method."""
    self.bpt = Bpt()

  def run(self, argv):
    """Command-line processor.

    Arguments:
      argv: Pass sys.argv from main.
    """
    parser = argparse.ArgumentParser()
    subparsers = parser.add_subparsers(title='subcommands')

    sub_parser = subparsers.add_parser(
        'version',
        help='Prints version of bpttool.')
    sub_parser.set_defaults(func=self.version)

    sub_parser = subparsers.add_parser(
        'make_table',
        help='Lays out partitions and creates partition table.')
    sub_parser.add_argument('--input',
                            help='Path to partition definition file.',
                            type=argparse.FileType('r'),
                            action='append')
    sub_parser.add_argument('--ab_suffixes',
                            help='Set or override A/B suffixes.')
    sub_parser.add_argument('--partitions_offset_begin',
                            help='Set or override disk partitions '
                                 'offset begin size.',
                            type=ParseSize)
    sub_parser.add_argument('--disk_size',
                            help='Set or override disk size.',
                            type=ParseSize)
    sub_parser.add_argument('--disk_alignment',
                            help='Set or override disk alignment.',
                            type=ParseSize)
    sub_parser.add_argument('--disk_guid',
                            help='Set or override disk GUID.',
                            type=ParseGuid)
    sub_parser.add_argument('--output_json',
                            help='JSON output file name.',
                            type=argparse.FileType('w'))
    sub_parser.add_argument('--output_gpt',
                            help='Output file name for MBR/GPT/GPT file.',
                            type=argparse.FileType('w'))
    sub_parser.set_defaults(func=self.make_table)

    sub_parser = subparsers.add_parser(
        'make_disk_image',
        help='Creates disk image for loaded with partitions.')
    sub_parser.add_argument('--output',
                            help='Path to image output.',
                            type=argparse.FileType('w'),
                            required=True)
    sub_parser.add_argument('--input',
                            help='Path to bpt file input.',
                            type=argparse.FileType('r'),
                            required=True)
    sub_parser.add_argument('--image',
                            help='Partition name and path to image file.',
                            metavar='PARTITION_NAME:PATH',
                            action='append')
    sub_parser.add_argument('--allow_empty_partitions',
                            help='Allow skipping partitions in bpt file.',
                            action='store_true')
    sub_parser.set_defaults(func=self.make_disk_image)

    sub_parser = subparsers.add_parser(
        'query_partition',
        help='Looks up informtion about a partition.')
    sub_parser.add_argument('--input',
                            help='Path to partition definition file.',
                            type=argparse.FileType('r'),
                            required=True)
    sub_parser.add_argument('--label',
                            help='Label of partition to look up.',
                            required=True)
    sub_parser.add_argument('--ab_collapse',
                            help='Collapse A/B partitions.',
                            action='store_true')
    sub_parser.add_argument('--type',
                            help='Type of information to look up.',
                            choices=QUERY_PARTITION_TYPES,
                            required=True)
    sub_parser.set_defaults(func=self.query_partition)

    args = parser.parse_args(argv[1:])
    args.func(args)

  def version(self, _):
    """Implements the 'version' sub-command."""
    print '{}.{}'.format(BPT_VERSION_MAJOR, BPT_VERSION_MINOR)

  def query_partition(self, args):
    """Implements the 'query_partition' sub-command."""
    try:
      result = self.bpt.query_partition(args.input,
                                        args.label,
                                        args.type,
                                        args.ab_collapse)
    except BptParsingError as e:
      sys.stderr.write('{}: Error parsing: {}\n'.format(e.filename, e.message))
      sys.exit(1)
    except BptError as e:
      sys.stderr.write('{}\n'.format(e.message))
      sys.exit(1)

    if not result:
      sys.stderr.write('No partition with label "{}".\n'.format(args.label))
      sys.exit(1)

    print result

  def make_table(self, args):
    """Implements the 'make_table' sub-command."""
    if not args.input:
      sys.stderr.write('Option --input is required one or more times.\n')
      sys.exit(1)

    try:
      (json_str, gpt_bin) = self.bpt.make_table(args.input, args.ab_suffixes,
                                                args.partitions_offset_begin,
                                                args.disk_size,
                                                args.disk_alignment,
                                                args.disk_guid)
    except BptParsingError as e:
      sys.stderr.write('{}: Error parsing: {}\n'.format(e.filename, e.message))
      sys.exit(1)
    except BptError as e:
      sys.stderr.write('{}\n'.format(e.message))
      sys.exit(1)

    if args.output_json:
      args.output_json.write(json_str)
    if args.output_gpt:
      args.output_gpt.write(gpt_bin)

  def make_disk_image(self, args):
    """Implements the 'make_disk_image' sub-command."""
    if not args.input:
      sys.stderr.write('Option --input is required.\n')
      sys.exit(1)
    if not args.output:
      sys.stderr.write('Option --ouptut is required.\n')
      sys.exit(1)

    try:
      self.bpt.make_disk_image(args.output,
                               args.input,
                               args.image,
                               args.allow_empty_partitions)
    except BptParsingError as e:
      sys.stderr.write('{}: Error parsing: {}\n'.format(e.filename, e.message))
      sys.exit(1)
    except 'BptError' as e:
      sys.stderr.write('{}\n'.format(e.message))
      sys.exit(1)

if __name__ == '__main__':
  tool = BptTool()
  tool.run(sys.argv)